The present invention is directed to weight measuring apparatus and more particularly to a method for automatically zero balancing a weighing scale so as to meet Federal standards concerning the accuracy of the scale for measuring weights placed on the scale.
Weighing scales are found in supermarkets or the like for weighing produce or other merchandise items and must meet stringent requirements as to performance and cost. The scales must be accurate enough to satisfy public weights and measures authorities. These requirements are usually met at the time the scale is manufactured by means of a calibrating procedure. As part of these requirements, the scale must display a predetermined reference value, normally zero, when no merchandise item is being weighed so that the change in the output display produced by a merchandise item being weighed will accurately represent the true weight of the item. Through use, the zero reference of the scale may change due to the following causes: the accumulation of foreign matter on the scale platform or its supports; a change in the position of the scale platform; the effect of temperature on the electronic components; the offset due to aging of the electrical components; and hystersis, especially after weighing of a heavy object. Prior methods for zero balancing a scale have included the manual setting of control linkages or the like to zero balance the scale. This procedure was slow and cumbersome, thereby detracting from the usefulness of the scale in check-out operations.
It is therefore a principal object of this invention to provide a method for zero balancing a weighing scale which is simple in its operation and can be accomplished in a minimum amount of time.